It has long been known that the unique crystalline structure of graphite makes it anisotropic with respect to conducting electrons. Its structure basically comprises planes of aromatically bound carbon atoms. Hence, each of such planes has .pi. clouds of electrons above and below it. These electron clouds have been said to contribute to its anisotropic conductive behavior, the conductivity being in a direction parallel to the aromatic carbon planes. This conductivity is approximately 5 percent that of copper.
It also has been known that certain elements or molecules, when diffused into the graphite lattice, assume positions interstitial to the aromatic planes and improve graphite conductivity. Ubbeholde, for example, found that the interstitial compound formed between graphite and nitric acid has a conductivity almost equal to that of copper (which is 0.6.times.10.sup.6 ohms.sup.-1 cm.sup.-1) when measured parallel to the aromatic planes (A. R. Ubbeholde, Proc. Roy. Soc., A304, 25, l968).
U.S. Pat. No. 3,409,563 granted to Olstowski describes conductive graphite structures formulated from vermicular graphite and an agent such as Br.sub.2, FeCl.sub.3, CrO.sub.2 Cl.sub.2, SO.sub.3 SbCl.sub.5, CrCl.sub.3, ICl, CrO.sub.3, AuCl.sub.3, InCl.sub.3, PtCl.sub.4, CrO.sub.2 F.sub.2, TaCl.sub.5, SmCl.sub.3, ZrCl.sub.4, UCl.sub.4, and YCl.sub.3. The treated vermicular graphite is then compressed into structures.
In my copending U.S. Ser. No. 499,834, filed Aug. 23, 1974, is disclosed the formation of an electrically conductive graphite intercalation compound employing a strong acid halide system wherein graphite is reacted with "the proton donor (Bronsted acid), hydrogen fluoride, and an electron acceptor (Lewis acid) such as boron trihalide, a tetrahalide from a Group IV metal, or a pentahalide from a Group V metal." My German Pat. No. 2,537,272 which was published on Mar. 4, 1976 is a counterpart of the above-mentioned U.S. Ser. No. 499,834.
As discussed in detail hereafter the presently claimed invention contemplates the utilization of fluorosulfonic acid, i.e. HSO.sub.3 F, (sometimes designated "fluorosulfuric acid") or the closely related chlorosulfonic acid in combination with antimony pentafluoride or similar halide to form a graphite intercalation compound. The nature of this system, inter alia, is discussed in "Friedel-Crafts and Related Reactions" edited by George A. Olah, Interscience Publishers (1963). See particularly Chapter III by R. J. Gillespie at Page 191 where it is stated with respect to a fluorosulfuric acid/antimony pentafluoride system: "No simple proton acids are known in this system but SbF.sub.5 has been found to exhibit acid behavior by ionizing according to the equation EQU SbF.sub.5 +2HSO.sub.3 F=H.sub.2 SO.sub.3 F.sup.+ +SbF.sub.5 (SO.sub.3 F).sup.-."
Various acid systems are also discussed in "The Chemistry of Superacid Systems" by R. J. Gillespie appearing in Endeavour, Vol. XXXII (115), January 1973. Neither of the above R. J. Gillespie writings is directed to the formation of graphite intercalation compounds by any technique.
It is an object of the present invention to provide a novel graphite intercalation compound of relatively high electrical conductivity.
It is an object of the present invention to provide a novel process for the formation of a highly electrically conductive graphite intercalation compound.
It is a further object of the present invention to provide a novel process for preparing a highly electrically conductive graphite intercalation compound which readily can be formed in a carbonaceous fibrous material comprising graphitic carbon.
These and other objects, as well as the scope, nature, and utilization of the present invention will be apparent to those skilled in the art from the following detailed description and appended claims.